Nginx Solution for AWS Amazon ELB Health Checks - return 200 without IF

Question

I have the following code that is working on Nginx to keep the AWS ELB healthcheck happy.

map $http_user_agent $ignore {
  default 0;
  "ELB-HealthChecker/1.0" 1;
}

server {
  location / {
    if ($ignore) {
      access_log off;
      return 200;
    }
  }
}

I know the 'IF' is best avoided with Nginx and I wanted to ask if someone would know how to recode this without the 'if'?

thankyou

score 73 · Accepted Answer · answered Jun 25 '13 at 00:47

73

Don't overcomplicate things. Just point your ELB health checks at a special URL just for them.

server {
  location /elb-status {
    access_log off;
    return 200;
  }
}

answered Jun 25 '13 at 00:47

ceejayoz

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thankyou for you reply... can you explain a touch more... currently in the ELB health check I'm pointing it at /index.html. Do you mean point the health checks at say '/elb-status' and the add the above server block? is that it? does the /elb-status url need to exist? thx again – Adam Jun 25 '13 at 00:52
worked perfectly when I put /elb-status in the ELB and added the server block above - thankyou so much!!! greatly apprecated – Adam Jun 25 '13 at 00:58
Glad I could help! – ceejayoz Jun 25 '13 at 01:26
@ceejayoz, that was a clever solution. I spun up an instance that is getting no outside traffic, and one the elb status checks are taken care of, this starts to show up in the log, I think it is the ELB latency checks, any ideas there? 10.244.162.24 - - [26/Dec/2013:06:04:18 +0000] "-" 400 0 "-" "-" – eezis Dec 26 '13 at 06:14
1

Hmm, I'm gettting `"/usr/share/nginx/html/elb-status" failed (2: No such file or directory)`... any idea why this could be? – Michael Waterfall Jan 24 '14 at 17:47
@MichaelWaterfall If you do `curl -I http://localhost/elb-status` from the server, does it give you a 200? – ceejayoz Jan 24 '14 at 18:20
@MichaelWaterfall i have seen the same issue and an nginx restart seems to fix, but this is obviously no good when we want to auto scale our instances – Mark Unsworth May 27 '14 at 12:57
1

Neat solution. – pTK Sep 20 '17 at 08:00
Working fine. Does the access log of nginx shows this request ? Not showing up for me. – Sandeep Balagopal May 04 '20 at 16:14
1

@SandeepBalagopal See that `access_log off` line? – ceejayoz May 04 '20 at 16:19

score 31 · Answer 2 · answered Aug 03 '15 at 20:38

Just to improve on the above answer, which is correct. The following works great:

location /elb-status {
    access_log off;
    return 200 'A-OK!';
    # because default content-type is application/octet-stream,
    # browser will offer to "save the file"...
    # the next line allows you to see it in the browser so you can test 
    add_header Content-Type text/plain;
}

Babu · Answer 3 · 2017-01-05T23:59:51.363

Update: If the user agent validation is necessary,

set $block 1;

# Allow only the *.example.com hosts. 
if ($host ~* '^[a-z0-9]*\.example\.com$') {
   set $block 0;
}

# Allow all the ELB health check agents.
if ($http_user_agent ~* '^ELB-HealthChecker\/.*$') { 
  set $block 0;
}

if ($block = 1) { # block invalid requests
  return 444;
}

# Health check url
location /health {
  return 200 'OK';
  add_header Content-Type text/plain;
}

Nginx Solution for AWS Amazon ELB Health Checks - return 200 without IF

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